CMS logoCMS event Hgg
Compact Muon Solenoid
LHC, CERN

CMS-PAS-TOP-17-016
Search for top+photon production in pp collisions at 13 TeV in the muon+jets channel
Abstract: A search for events with a single top quark produced in association with a photon is performed. The analysis is based on data corresponding to an integrated luminosity of 35.9 fb$^{-1}$ of pp collisions at $\sqrt{s} = $ 13 TeV recorded by the CMS experiment at the LHC in 2016. The events are selected by requiring the presence of a muon ($\mu$), a photon ($\gamma$), an undetected neutrino ($\nu$), and at least two jets (j) from which one is identified as a b jet. A multivariate analysis based on topological and kinematic properties is employed to discriminate the signal from the background processes. An excess above the background-only hypothesis is observed, with a significance corresponding to 4.4 standard deviations. A fiducial cross section is measured for photons with transverse momentum greater than 25 GeV and in the central region of the detector that are well separated from muons and jets. The measured cross section times branching fraction is $\mathcal{B}(\mathrm{ t \rightarrow\mu\nu b) \sigma (t \gamma j }) = $ 115 $\pm$ 17 (stat) $_{-27}^{+33}$ (syst) fb, which agrees with the standard model prediction.
Figures & Tables Summary References CMS Publications
Figures

png pdf
Figure 1:
Representative Feynman diagrams for single top quark production in association with a photon in the $t$ channel, including the leptonic decay of the W boson in the top quark decay.

png pdf
Figure 1-a:
Representative Feynman diagrams for single top quark production in association with a photon in the $t$ channel, including the leptonic decay of the W boson in the top quark decay.

png pdf
Figure 1-b:
Representative Feynman diagrams for single top quark production in association with a photon in the $t$ channel, including the leptonic decay of the W boson in the top quark decay.

png pdf
Figure 1-c:
Representative Feynman diagrams for single top quark production in association with a photon in the $t$ channel, including the leptonic decay of the W boson in the top quark decay.

png pdf
Figure 2:
Distributions of some of the input variables to the BDT: $\Delta R({\text light jet},\gamma)$ (top-left), cosine of the angle between the muon candidate and the light jet in the top quark rest frame (top-right), pseudorapidity of the light jet (bottom-left), and reconstructed top quark mass (bottom-right) after the final event selection for data (points), and the SM prediction (histograms). The hatched band shows the statistical and systematic uncertainties in the estimated signal and background yields and the vertical bars on the points represent the statistical uncertainties in data.

png pdf
Figure 2-a:
Distributions of some of the input variables to the BDT: $\Delta R({\text light jet},\gamma)$ (top-left), cosine of the angle between the muon candidate and the light jet in the top quark rest frame (top-right), pseudorapidity of the light jet (bottom-left), and reconstructed top quark mass (bottom-right) after the final event selection for data (points), and the SM prediction (histograms). The hatched band shows the statistical and systematic uncertainties in the estimated signal and background yields and the vertical bars on the points represent the statistical uncertainties in data.

png pdf
Figure 2-b:
Distributions of some of the input variables to the BDT: $\Delta R({\text light jet},\gamma)$ (top-left), cosine of the angle between the muon candidate and the light jet in the top quark rest frame (top-right), pseudorapidity of the light jet (bottom-left), and reconstructed top quark mass (bottom-right) after the final event selection for data (points), and the SM prediction (histograms). The hatched band shows the statistical and systematic uncertainties in the estimated signal and background yields and the vertical bars on the points represent the statistical uncertainties in data.

png pdf
Figure 2-c:
Distributions of some of the input variables to the BDT: $\Delta R({\text light jet},\gamma)$ (top-left), cosine of the angle between the muon candidate and the light jet in the top quark rest frame (top-right), pseudorapidity of the light jet (bottom-left), and reconstructed top quark mass (bottom-right) after the final event selection for data (points), and the SM prediction (histograms). The hatched band shows the statistical and systematic uncertainties in the estimated signal and background yields and the vertical bars on the points represent the statistical uncertainties in data.

png pdf
Figure 2-d:
Distributions of some of the input variables to the BDT: $\Delta R({\text light jet},\gamma)$ (top-left), cosine of the angle between the muon candidate and the light jet in the top quark rest frame (top-right), pseudorapidity of the light jet (bottom-left), and reconstructed top quark mass (bottom-right) after the final event selection for data (points), and the SM prediction (histograms). The hatched band shows the statistical and systematic uncertainties in the estimated signal and background yields and the vertical bars on the points represent the statistical uncertainties in data.

png pdf
Figure 3:
The BDT output distribution for data and SM predictions after the fit. The inset presents a zoom on the last three bins.
Tables

png pdf
Table 1:
Event yields after the event selection in data and for each SM contribution. The expected yields are presented with the statistical and systematic uncertainties combined.
Summary
References
1 M. Fael and T. Gehrmann Probing top quark electromagnetic dipole moments in single-top-plus-photon production PRD 88 (2013) 033003 1307.1349
2 S. M. Etesami, S. Khatibi, and M. Mohammadi Najafabadi Measuring anomalous WW $ \gamma $ and t $ \bar{\text {t}}\gamma $ couplings using top+$ \gamma $ production at the LHC EPJC 76 (2016) 533 1606.02178
3 CDF Collaboration Evidence for $ t\bar{t}\gamma $ Production and Measurement of $ \sigma_{t\bar{t}\gamma} / \sigma_{t\bar{t}} $ PRD 84 (2011) 031104 1106.3970
4 ATLAS Collaboration Measurement of the $ t\bar{t}\gamma $ production cross section in proton-proton collisions at $ \sqrt{s} = $ 8 TeV with the ATLAS detector JHEP 11 (2017) 086 1706.03046
5 CMS Collaboration Measurement of the semileptonic $ \mathrm{t}\overline{\mathrm{t}}+\gamma $ production cross section in pp collisions at $ \sqrt{s}= $ 8 TeV JHEP 10 (2017) 006 CMS-TOP-14-008
1706.08128
6 J. Alwall et al. The automated computation of tree-level and next-to-leading order differential cross sections, and their matching to parton shower simulations JHEP 07 (2014) 079 1405.0301
7 NNPDF Collaboration Parton distributions for the LHC Run II JHEP 04 (2015) 040 1410.8849
8 P. Nason A New method for combining NLO QCD with shower Monte Carlo algorithms JHEP 11 (2004) 040 hep-ph/0409146
9 S. Frixione, P. Nason, and C. Oleari Matching NLO QCD computations with Parton Shower simulations: the POWHEG method JHEP 11 (2007) 070 0709.2092
10 S. Alioli, P. Nason, C. Oleari, and E. Re A general framework for implementing NLO calculations in shower Monte Carlo programs: the POWHEG BOX JHEP 06 (2010) 043 1002.2581
11 J. M. Campbell, R. K. Ellis, P. Nason, and E. Re Top-Pair Production and Decay at NLO Matched with Parton Showers JHEP 04 (2015) 114 1412.1828
12 CMS Collaboration Event generator tunes obtained from underlying event and multiparton scattering measurements EPJC 76 (2016) 155 CMS-GEN-14-001
1512.00815
13 GEANT4 Collaboration GEANT4---a simulation toolkit NIMA 506 (2003) 250
14 CMS Collaboration Description and performance of track and primary-vertex reconstruction with the CMS tracker JINST 9 (2014) P10009 CMS-TRK-11-001
1405.6569
15 M. Cacciari, G. P. Salam, and G. Soyez The anti-$ k_t $ jet clustering algorithm JHEP 04 (2008) 063 0802.1189
16 M. Cacciari, G. P. Salam, and G. Soyez FastJet user manual EPJC 72 (2012) 1896 1111.6097
17 CMS Collaboration Identification of heavy-flavour jets with the CMS detector in pp collisions at 13 TeV JINST 13 (2018) P05011 CMS-BTV-16-002
1712.07158
18 CMS Collaboration Particle-flow reconstruction and global event description with the CMS detector JINST 12 (2017) P10003 CMS-PRF-14-001
1706.04965
19 CMS Collaboration Performance of photon reconstruction and identification with the CMS detector in proton-proton collisions at sqrt(s) = 8 TeV JINST 10 (2015) P08010 CMS-EGM-14-001
1502.02702
20 M. Cacciari and G. P. Salam Pileup subtraction using jet areas PLB 659 (2008) 119 0707.1378
21 CMS Collaboration Measurement of the $ t $-channel single top quark production cross section in $ pp $ collisions at $ \sqrt{s}= $ 7 TeV PRL 107 (2011) 091802 CMS-TOP-10-008
1106.3052
22 CMS Collaboration Measurement of $ W\gamma $ and $ Z\gamma $ production in $ pp $ collisions at $ \sqrt{s} = $ 7 TeV PLB 701 (2011) 535 CMS-EWK-10-008
1105.2758
23 CMS Collaboration Measurement of electroweak-induced production of W$ \gamma $ with two jets in pp collisions at $ \sqrt{s}= $ 8 TeV and constraints on anomalous quartic gauge couplings JHEP 06 (2017) 106 CMS-SMP-14-011
1612.09256
24 CMS Collaboration Jet algorithms performance in 13 TeV data CDS
25 CMS Collaboration Jet energy scale and resolution in the CMS experiment in pp collisions at 8 TeV JINST 12 (2017), no. 02, P02014 CMS-JME-13-004
1607.03663
26 CMS Collaboration Measurement of inclusive W and Z boson production cross sections in pp collisions at $ \sqrt{s} = $ 8 TeV PRL 112 (2014) 191802 CMS-SMP-12-011
1402.0923
27 CMS Collaboration Performance of CMS muon reconstruction in $ pp $ collision events at $ \sqrt{s}= $ 7 TeV JINST 7 (2012) P10002 CMS-MUO-10-004
1206.4071
28 CMS Collaboration Performance of electron reconstruction and selection with the CMS detector in proton-proton collisions at $ \sqrt{s}= $ 8 TeV JINST 10 (2015) P06005 CMS-EGM-13-001
1502.02701
29 CMS Collaboration Measurement of the $ W\gamma $ and $ Z\gamma $ inclusive cross sections in $ pp $ collisions at $ \sqrt{s} = $ 7  TeV and limits on anomalous triple gauge boson couplings PRD 89 (2014) 092005 CMS-EWK-11-009
1308.6832
30 CMS Collaboration Measurement of the inelastic proton-proton cross section at $ \sqrt{s}= $ 13 TeV Submitted to: JHEP (2018) CMS-FSQ-15-005
1802.02613
31 CMS Collaboration CMS luminosity measurement for the 2015 data taking period CMS-PAS-LUM-15-001 CMS-PAS-LUM-15-001
32 CMS Collaboration Measurement of the cross section for electroweak production of Z$ \gamma $ in association with two jets and constraints on anomalous quartic gauge couplings in proton–proton collisions at $ \sqrt{s} = $ 8 TeV PLB 770 (2017) 380 CMS-SMP-14-018
1702.03025
33 CMS Collaboration Measurement of the $ {{\mathrm{W}}^{+}}\mathrm{W}^{-} $ cross section in pp collisions at $ \sqrt{s} = $ 8 TeV and limits on anomalous gauge couplings EPJC 76 (2016)
34 CMS Collaboration Cross section measurement of $ t $-channel single top quark production in pp collisions at $ \sqrt s = $ 13 TeV PLB 772 (2017) 752 CMS-TOP-16-003
1610.00678
35 M. Bahr et al. Herwig++ Physics and Manual EPJC 58 (2008) 639 0803.0883
36 H. Voss, A. Hocker, J. Stelzer, and F. Tegenfeldt TMVA, the toolkit for multivariate data analysis with ROOT in XIth International Workshop on Advanced Computing and Analysis Techniques in Physics Research (ACAT), p. 40 2007 physics/0703039
Compact Muon Solenoid
LHC, CERN